Drive circuit for electronic counters with means to prevent spurious switching



June 4, 1963 R W. WO

LFE DRIVE CIRCUIT FOR ELECTRONIC COUNTERS WITH MEANS TO PREVENT SPURIOUSSWITCHING Filed May 23, 1960 SET 42 5 J H I 56 32 /6 E- w M F V /6 -2053 /52 CATHODE FOLLOWER CATHODE FOLLOWER 54 SWITCHING SIGNAL I soupcs 45 INVENTOR;

ROGER W WOLFE ATTORNEY 21511 MEANS TO PREVENT SPURIOUS SWITCH- Roger W.Wolfe, South Plainfield, NJ., assignor to Burroughs Corporation,Detroit, Mich., a corporation of Michigan Filed May 23, 1960, Ser. No.30,966 4 Claims. (Cl. 3158.5)

This invention relates to drive circuits for electronic countingcircuits and particularly to counting circuits using multi-positionelectron beam tubes as the basic counting unit.

One type of electronic counter utilizes a multi-position magnetron beamswitching tube which includes an electrode assembly comprising a centralcathode and a plurality of groups of electrodes surrounding the cathode.Each of the groups of electrodes comprises a position to which anelectron beam may flow and from which an output signal may be derived.Suitable magnet means provides a longitudinal magnetic field whichcombines with electronic fields within the tube to provide the desiredswitching action. According to one method of operation, a flip-flop isemployed to drive an electron beam from position to position in thetube. However, it has been found that, under some circumstances, forexample where the flip-flop is plate-triggered, or when the flip-flop ischanging state, undesired or spurious switching of the tube occurs.

Accordingly, the principles and objects of the present invention aredirected toward the provision of an improved driving circuit for amulti-position beam switching tube wherein spurious switching of thetube is prevented.

Briefly, the circuit of the invention includes a mgnetron beam switchingtube of the type described above in which each group of electrodesincludes a target electrode to which an electron beam flows and fromwhich an output signal is derived, a spade electrode which holds anelectron beam on its associated target electrode, and a switchingelectrode which is used to switch a beam from one position to the next.The switching electrodes are connected in two sets, with alternateelectrodes being connected together, and a driving circuit is coupled tothe sets of switching electrodes. The driving circuit is of a type whichmay generate transient pulses which may cause spurious switching of thetube. According to the invention, means are provided for rendering thetube more difiicult to switch during the period when the driving eansmight generate transient pulses and before the desired stable switchingstate has been reached. After this time has passed, the stable,steady-state pulses generated by the driving circuit cause the desiredand normal switching operation.

The invention is described in greater detail by reference to the drawingwherein the single FIGURE is a schematic representation of a countingtube and a circuit in which it may be operated according to theinvention.

The circuit described below is particularly suitable for use with amulti-position type 6700 magnetron beam switching tube. In actualconstruction, this type of tube is cylindrical in form but is shownschematically in linear form as tube It) in the drawing. The tubeincludes an envelope 12 which contains a central longitudinallyelongated cathode 14- and ten groups of electrodes spaced radiallyequidistantly from the cathode and surrounding the cathode. Forsimplicity, only four groups of electrodes are shown numbered 0, 1, 8,and 9. Each group of electrodes includes a generally U-shaped elongatedspade electrode 16 and a generally L-shaped target electrode 18positioned so that each target occupies the space 3,092,752 PatentedJune 4, 1963 between adjacent spade electrodes. Each spade electrodeserves to form and hold an electron beam on its correponding targetelectrode. A generally rod-like switching electrode 20 is also includedin each group of electrodes and is positioned between one edge of eachtarget electrode and the adjacent spade electrode. The switchingelectrodes are known as switching grids. An open-ended cylindricalpermanent magnet represented schematically at 22 is provided surroundingthe tube envelope and coaxial therewith. The magnet 22 provides an axialmagnetic field which is utilized in conjunction with electric fieldswithin the tube to form and switch an electron beam from the cathode toeach of the groups of electrodes. The direction in which the beamswitches, that is clockwise or counterclockwise, is always the same andis determined by the orientation of the electric and magnetic fields.

Briefly, in operation of tube 10, electrons emitted by the cathode areretained at the cathode if each of the spades, targets and switchinggrids carries its normal operating electrical potential. When a spade orswiching grid experiences a suitable lowering of its potential, anelectron beam is formed and directed to the corresponding targetelectrode. The electron beam may be switched from one target electrodeto the next by thus suitably altering the electrical potentials of aspade or switching grid. Under normal operating conditions, wheneverelectrode voltages are such that a beam might be supported at severalpositions, the beam will switch to themost leading position and lock inat this position.

In the circuit shown, the cathode 14 is connected through a suitablebias resistor 24 to ground. Each of the spade electrodes 16 is coupledthrough a spade load resistor 26 to a spade buss 28. The spade buss 28is coupled through a common spade resistor 30- to a suitable positiveDC. power supply V of about 200 volts. -A suitable zero-set circuit 32for clearing an electron beam in the tube and resetting it at the 0position is coupled to the spade buss 28 and the spade electrode 16 atthe 0 position. A typical zero-set circuit operates by first reducingthe potential of the spade buss to a level at which a beam cannot bemaintained at any position and then holding the 0 spade at a lowervoltage level than the other spades until a beam forms at the 0position. Of course, any desired and suitable zero-set arrangement maybe used.

The target electrodes 18 are connected through suitable load resistors38 to a common target buss 49 which is coupled to a positive DC. powersupply V of about 300 volts. In addition, an auxiliary output tap 42 isprovided at each target for connection to a suitable utilization devicesuch as an indicator tube, a printing mechanism 'or the like, ifdesired.

The switching grid electrodes 28 are connected in two sets, with thegrids at the even-numbered positions connected together in one set andthe grids at the odd-numbered positions connected together in anotherset.

Apparatus for driving the beam switching tube and switching an electronbeam from position to position includes a source 44 of switching signals(negative pulses) which is coupled through a capacitor 45 to the plateelectrodes of a conventional flip-cfiop circuit 46. The signal source isthus adapted to plate-trigger the flip-flop circuit. This method ofdriving a flip-flop is well known, and the elements of a typicalflip-flop are shown without being described in detail. The flip-flopincludes two output leads 4S and 50, one of which is connected to theinput of a cathode follower circuit 52, the output of which is coupledby lead 53 to one of the sets of switching electrodes and the other ofwhich is connected to the input of a cathode follower 54, the output ofwhich is connected by lead 55 to the other set of switching electrodes.The

cathodefollower circuits are conventional and are not shown in detail.According to the invention, the signal source, in addition to beingcoupled to the plates of the flip-flop circuit 46, is also coupledthrough a capacitor 56 to the spade buss 28. The capacitor thus isadapted ,to couple a portion of the input switching signal to the spadebuss.

In operation of the invention, when a switching pulse is applied fromthe signal source 44 to the plate circuit of the flip-flop 46, the samenegative pulse is transmitted in part to the spade buss 28. Thus, thespade buss is lowered in potential by about 25 volts. This reduction inpotential of the spade buss makes it more difficult to switch anelectron beam during the short time in which the fiip-flop andthecathode followers are changing state. Thus, spurious switching duringthis time due to transient pulses or the like is prevented and desiredswitching occurs when these components have completed their change instate and the proper stable, steady-state switching pulse is 7 appliedto the appropriate switching electrode. 7

In operation of the invention, the magnitude of the switching pulsesapplied to the flip-fiop from the source 44 is deter-mined by therequirements of the flip-flop. In addition, the magnitude of the pulsecoupled to the spade buss should be large enough only to resist spuriousswitching and should not be so large that the tube is cleared.

It is clear that the principles of the invention, whereby spuriousswitching of an electron beam is prevented, may be practiced whereappropriate with other types of driving circuits and the invention isnot limited to plate-driver flip-flops or flip-flops operated withcathode follower circuits. 7

What is claimed is:

1. A counter circuit including a magnetron type electron beam switchingtube having a cathode and a plurality of' groups of electrodes; eachgroup including a target electrode which receives an electron beam andproduces an output signal therefrom, a spade electrode which holds anelectron beam on its associated target electrode, and a switchingelectrode which serves to switch an electron beam from one group ofelectrodes to the next; means providing a longitudinal magnetic field insaid tube; said switching electrodes being connected in two sets withalternate electrodes being connected together; flip-flop driving meanscoupled to said sets of switching electrodes; and switching signal inputmeans coupled both to said flip-flop and to the spade electrodes of saidbeam switching tube whereby a switching signal is applied to saidflip-flop and to said beam tube at the same time; said signal renderingsaid beam'tube temporarily difiicult to switch during the time when saidflip-flop is changing states to provide desired steady-state switchingof the tube.

2. A counter circuit including an electron beam switching tube having acathode and a plurality of groups of electrodes; each group ofelectrodes including a target electrode which receives an electron beamand produces an output signal therefrom, a spade electrode which holdsan electron beam on its associated target electrode, and a switchingelectrode which serves to switch an electron beam from one group ofelectrodes to the next; drive circuit means coupledto said tube forapplying steady-state stable switching pulses't-hereto and thus causingan electron beam to switch from position to position;

and auxiliary circuit means coupled from said drive circuit means tosaid spade electrodes and applying a small negative potential theretofor rendering said tube. temporarily diificult to switch wherebytransient pulses from said drive circuit do not cause spuriousswitching. 3. A circuit defined in claim 2 wherein said drive circuitmeans is coupled to the switching electrodes of said tube.

4. A counter circuit including an electron beam switching tube having acathode and a plurality of groups of electrodes; each group including atarget electrode which receives an electron beam and produces an outputsignal therefrom, a spade electrode which holds an electron beam on itsassociated target electrode, and a switching electrode which serves toswitch an electron beam from one group of electrodes to the next; saidswitching electrodes being connected in two sets with alternateelectrodes being connected together; circuit driving means coupled tosaid sets of switching electrodes; and driving signal input meanscoupled both to said circuit driving means and to the spade electrodesof said beam switching tube whereby a portion of the driving signal iscoupled to the spade electrodes of said tube and renders the tubediflicult to switch during a portion of the time when said circuitdriving means is energized by said driving signal.

References Cited in the file 'of this patent UNITED STATES PATENTS

1. A COUNTER CIRCUIT INCLUDING A MAGNETRON-TYPE ELECTRON BEAM SWITCHINGTUBE HAVING A CATHODE AND A PLURALITY OF GROUPS OF ELECTRODES; EACHGROUP INCLUDING A TARGET ELECTRODE WHICH RECEIVES AN ELECTRON BEAM ANDPRODUCES AN OUTPUT SIGNAL THEREFROM, A SPADE ELECTRODE WHICH HOLDS ANELECTRON BEAM ON ITS ASSOCIATED TARGET ELECTRODE, AND A SWITCHINGELECTRODE WHICH SERVES TO SWITCH AN ELECTRON BEAM FROM ONE GROUP OFELECTRODES TO THE NEXT; MEANS PROVIDING A LONGITUDINAL MAGNETIC FIELD INSAID TUBE; SAID SWITCHING ELECTRODES BEING CONNECTED IN TWO SETS WITHALTERNATE ELECTRODES BEING CONNECTED TOGETHER; FLIP-FLOP DRIVING MEANSCOUPLED TO SAID SETS OF SWITCHING ELECTRODES; AND SWITCHING SIGNAL INPUTMEANS COUPLED BOTH TO SAID FLIP-FLOP AND TO THE SPADE ELECTRODES OF SAIDBEAM SWITCHING TUBE WHEREBY A SWITCHING SIGNAL IS APPLIED TO SAIDFLIP-FLOP AND TO SAID BEAM TUBE AT THE SAME TIME; SAID SIGNAL RENDERINGSAID BEAM TUBE TEMPORARILY DIFFICULT TO SWITCH DURING THE TIME WHEN SAIDFLIP-FLOP IS CHANGING STATES TO PROVIDE DESIRED STEADY-STATE SWITCHINGOF THE TUBE.